Post-Print Annealing: A Simple Strategy for Enhancing Adhesion in FDM-printed PLA-SMA Composites

Embedding Shape Memory Alloy (SMA) wires within 3D printed polymers enables 4D printing, but achieving strong interfacial adhesion is challenging without complex surface treatments. This study aims to investigate a simple post-print annealing strategy to enhance the adhesion between SMA wires and 3D-printed artefacts. SMA wires were embedded in FDM-printed PLA cylinders. A full factorial Design of Experiments was conducted, varying annealing temperatures (90, 110, 130 °C) and time (30, 60, 90 min). Adhesion was quantified via pull-out tests measuring Interfacial Shear Strength (ISS). Volumetric changes and degree of crystallinity by Differential Scanning Calorimetry were assessed. Tensile tests evaluated annealing effects on PLA properties. Annealing temperature significantly increased ISS, driven by increased PLA crystallinity (up to ≈ 49.2 %) and volumetric shrinkage (≈ 1.2 %). Annealing time had a negligible effect. Optimal conditions (130 °C, 60 min) achieved a significant increase in pull-out force for annealed specimens (ISS ≈ 0.8 MPa) compared to not annealed ones (ISS ≈ 0.3 MPa). Tensile tests on PLA revealed that annealing increased Young’s Modulus with increased temperatures but decreased ductility and tensile strength. Prolonged annealing (130 °C, 90 min) showed slightly reduced ISS, potentially due to polymer relaxation/degradation. This easily implementable annealing method offers a way to create more robust and reliable 4D printed SMA-polymer actuators and composites using standard FDM printers.